A fragile and invisible layer of ozone some nine to fifty kilometers above shields the earth's surface against harmful ultraviolet radiation from the sun. It has been discovered that this protective shield is being massively depleted. Such is generally accepted to largely be the result of man-made chemicals that have been and continue to be released into the atmosphere.
Ozone is naturally produced in the stratosphere. Molecular oxygen, O.sub.2, is naturally photodissociated into free oxygen atoms under the influence of radiation from the sun. Such production of oxygen atoms leads immediately to the production of ozone molecules as shown in the following equation, EQU O.sub.2 +O+M.fwdarw.O.sub.3 +M,
where a triple collision between a molecule of oxygen O.sub.2, an atom of oxygen O, and a third particle "M", which may be a molecule of oxygen or of nitrogen, which absorbs excess reaction energy and results in formation of a molecule of ozone, O.sub.3.
Ozone-depleting chemicals fall into four major groups. The first is known as chlorofluorocarbons (CFC's). These are used as aerosol propellants, refrigerants, blowing agents, solvents and sterilants. Freon-12 (dichlorodifluoromethane) is one example. A second group is known as "halons", which are bromine-containing chemicals used as fire suppressants. A third group is known as chlorocarbons, and include chemicals such as carbon tetrachloride and 1,1,1-trichloromethane. A fourth group consists of relatives of the CFC's called "hydrochlorofluorocarbons" (HCFC's). These are widely used as interim substitutes for some CFC's, and typically have from 2% to 10% of the ozone-destroying power of CFC's.
When released during production and use, it is believed that ozone-depleting chemicals remain in the atmosphere for decades, some even for centuries. Once released, they are atmospherically heated, wind and air current dispersed, and ultimately rise to 10 to 15 kilometers. There, ultraviolet light in the wavelength range of from 170 to 230 nanometers breaks the molecules apart. This releases chlorine, fluorine or bromine which contribute to the destruction of ozone and the formation of ordinary oxygen, a substance which is useless for screening out dangerous ultraviolet radiation from the sun.
Once the molecules are broken, some of the fluorine combines with hydrogen to form HF. Ultimately, the fluorine is precipitated into the lower atmosphere where it ends up in water solution. Carbon freed from the halogenated organic compounds combines with available oxygen to form CO.sub.2. Such is chemically benign, but physically contributes to global warming which is commonly referred to as the "greenhouse effect". Also, the gaseous halogenated organic compounds while in the lower atmosphere on their way to the stratosphere are believed to themselves absorb infrared radiation reflected from the earth's surface, thereby converting it into heat and contributing to global warming. Ozone-depleting chemicals are believed responsible for 20% to 25% of current increases in the greenhouse effect.
Combination of carbon with free oxygen to form CO.sub.2 is also believed to adversely affect O.sub.3 production. The carbon in essence consumes some of the raw material (free oxygen) out of which O.sub.3 is naturally made in the atmosphere.
Free chlorine atoms from the ultraviolet light dissociation of the halogenated organic gases would have a tendency to combine with one another to form chlorine gas (Cl.sub.2), but for available free oxygen atoms available in the atmosphere. The pollutant chlorine atoms have a greater tendency to join with free oxygen atoms to form a chlorine oxide (ClO.sub.x), again consuming one of the principal raw material (free oxygen) out of which O.sub.3 is made.
As the ozone layer is depleted, more harmful ultraviolet radiation reaches the earth's surface. Unless ozone depletion is stopped, adverse global health and environmental consequences on a large scale are predicted to occur. The Environmental Protection Agency (EPA) has predicted that increased ultraviolet radiation from ozone depletion would cause between 163,000,000 and 308,000,000 extra cases of skin cancer in the U.S. alone, among people alive today and born by 2075, if nothing were done to save the ozone layer. About 3.5 to 6.5 million of these cases are predicted to be fatal. More ultraviolet radiation would also cause an estimated 19 to 29 million additional cases of cataracts in this population. Sharp increases in the number and variety of serious immunological disorders are also predicted. Further, damage to the natural environment from increased ultraviolet radiation would range from billions of dollars in reduced crop yields to disruption of the marine food chain.
It is not surprising then that research is underway for substitutes for these gaseous halogenated organic compounds. However, it is estimated that it may take 20 years or more to find acceptable substitutes. Consider that the substitute will need to be benign, non-flammable, stable, inexpensive and safe for use in homes (i.e. for refrigeration and aerosol propellants). Accordingly, people are as well working on techniques for preventing these gaseous halogenated organic compounds from entering the atmosphere.
One potentially promising technique for avoiding release of these gases exposes the objectionable materials to ultraviolet radiation for destruction under controlled conditions. Examples of such techniques are disclosed in U.S. Pat. No. 4,210,503 to Confer and U.S. Pat. No. 4,045,316 to Legan. However, a problem associated with any such reactive systems is how one disposes of the reaction byproducts which are produced by the photochemical oxidation. While CFC's and HCFC's are rather inert to humans, the oxidation products produced by such reactors are very harmful to life. Additionally, the oxidation products can be corrosive, explosive or otherwise harmful or destructive to the reactor system and its components. Accordingly, it would be desirable to develop alternate methods and techniques for contending with the hazardous oxidation byproducts produced by such photochemical oxidations.